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Function to return an RSS feed using the (unofficial) Google Reader API

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GoogleReader.R
R
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require(XML)
require(RCurl)
 
#' This function ruturns an XML tree of the RSS feed from the given URL.
#'
#' This function utilizes the (unofficial) Google Reader API to retrieve RSS
#' feeds. The advantage of access RSS feeds through the Google Reader API is that
#' you are not limited by the number of entries a website may included in their
#' feed. That is, Google maintains generally maintains a complete history of
#' entries from the RSS feed.
#'
#' Note that the contents of the results will be limited by what the website
#' provides in their feeds. That is, Google does not contain more information
#' per entry then what the website originally provided. If the initial feed
#' contained only excerpts of the article, the feed from Google will too only
#' contain excerpts. Be aware though that for sites that do provide the complete
#' contents of posts will result in potentially very large downloads.
#'
#' @param feedURL the full URL to the RSS feed.
#' @param email the email address for the Google Reader account
#' @param passwd the password for the Google Reader account
#' @param posts the number of posts to return
#' @return the root \code{XMLNode} for the RSS feed.
#' @seealso \code{\link{/xmlRoot}} for the format of the returned XML tree
#' @export
#' @example
#' \dontrun{
#' rbloggers = getRSSFeed(feedURL="http://r-bloggers.com/feed",
#' email="USERNAME@gmail.com", passwd="PASSWORD")
#' }
#' @author Jason Bryer <\email{jason@@bryer.org}x>
getRSSFeed <- function(feedURL, email, passwd, posts=1000) {
#Authenticate with Google
curlHandle = getCurlHandle(cookiefile="rcookies", ssl.verifyhost=FALSE, ssl.verifypeer=FALSE)
x = postForm("https://www.google.com/accounts/ClientLogin",
accountType="GOOGLE",
service="reader",
Email=email,
Passwd=passwd,
source="makeR",
curl = curlHandle)
gtoken = unlist(strsplit(x, "\n"))
parsed.gtoken <- unlist(strsplit(gtoken[3], "Auth="))
if (length(parsed.gtoken) >= 2) {
auth.token <- unlist(strsplit(gtoken[3], "Auth="))[[2]]
} else {
stop("Authentication failed.")
}
google.auth <- paste("GoogleLogin auth=", auth.token, sep='')
#Function to retrieve up to 1000 posts
getDoc <- function(n, c=NULL) {
feedURL = paste("http://www.google.com/reader/atom/feed/", feedURL, "?n=", n,
ifelse(is.null(c), "", paste("&c=", c, sep='')),
sep='')
feed = getURL(feedURL, .encoding = 'UTF-8', followlocation=TRUE,
httpheader=c("Authorization"=google.auth),
curl=curlHandle)
doc = xmlTreeParse(feed, asText=TRUE)
return(xmlRoot(doc))
}
root = NULL
continueValue = NULL
for(i in 1:ceiling(posts / 1000)) {
r = getDoc(n=ifelse(i == ceiling(posts / 1000), (posts-1) %% 1000 + 1, 1000),
c=continueValue)
if(is.null(root)) {
root = r
} else {
entries = which(xmlSApply(r, xmlName) == 'entry')
if(length(entries) > 0) {
root = addChildren(root, kids=r[entries])
}
}
if(is.null(r[['continuation']])) {
break #No more posts to retrieve
} else {
continueValue = unclass(xmlChildren(r[['continuation']])$text)$value
}
}
return(root)
}

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